Multi-stage well isolation and fracturing

ABSTRACT

In a first aspect, a frac valve tool is taught, said tool comprising one or more ports a sleeve movable between a closed position in which the sleeve prevents fluid flow through said one or more ports and an open position in which the sleeve allows fluid flow through said one or more ports and a ball receiving seat removably connected to the sleeve wherein receipt of a ball on the ball receiving seat moves said seat and said sleeve from closed to open positions. In a second aspect, a frac valve tool is taught, said tool comprising a ball receiving seat removably received within said tool, said seat comprising a seating profile for receiving a ball; wherein said seating profile matches a radius of said ball to nondeformably grip said ball.

FIELD OF INVENTION

The present invention relates to devices for multi-stage, horizontalwell isolation and fracturing.

BACKGROUND OF THE INVENTION

An important challenge in oil and gas well production is accessinghydrocarbons that are locked in formation and not readily flowing. Insuch cases, treatment or stimulation of the formation is necessary tofracture the formation and provide passage of hydrocarbons to thewellbore, from where they can be brought to the surface and produced.

Fracturing of formations via horizontal wellbores traditionally involvespumping a stimulant fluid through either a cased or open hole section ofthe wellbore and into the formation to fracture the formation andproduce hydrocarbons therefrom.

In many cases, multiple sections of the formation are desirablyfractured either simultaneously or in stages. Tubular strings for thefracing of multiple stages of a formation typically include one or morefracing tools separated by one or more packers.

In some circumstances frac systems are deployed in cased wellbores, inwhich case perforations are provided in the cemented in system to allowstimulation fluids to travel through the fracing tool and the perforatedcemented casing to stimulate the formation beyond. In other cases,fracing is conducted in uncased, open holes.

In the case of multistage fracing, multiple frac valve tools are used ina sequential order to frac sections of the formation, typically startingat a toe end of the wellbore and moving progressively towards a heel endof the wellbore. It is crucial that the frac valves be triggered in thedesired order and that they do not open earlier than desired. Once open,it is also important that the frac valves do not become closed until itis desirable to close them.

Many configurations have been developed in the field to frac multiplestages of a formation. For example fracing tools are known in which aball is pumped into the tool and sits in a seat to block fluid flowthrough the central bore, thereby causing fluid pressure to build up andforcing fluid to flow through multiple jet nozzles locatedcircumferentially around the liner.

Other frac valve tools are known for use with coiled tubing, in which aball is dropped to block flow down the liner and redirect flow throughpressure firing heads in a fracking sleeve. Some downhole tools teachincluding a packer with a ball seat and a ball, in which fluid can beredirected to fracking ports on a fracing tool. Others teach the use ofballs of different sizes to control downhole surge pressure.

A need still however exists for frac valve tools that are simple inconstruction, small in size and effective at fracing formations inmultiple stages

SUMMARY OF THE INVENTION

In a first aspect, a frac valve tool is taught, said tool comprising oneor more ports a sleeve movable between a closed position in which thesleeve prevents fluid flow through said one or more ports and an openposition in which the sleeve allows fluid flow through said one or moreports and a ball receiving seat removably connected to the sleevewherein receipt of a ball on the ball receiving seat moves said seat andsaid sleeve from closed to open positions.

In a second aspect, a frac valve tool is taught, said tool comprising aball receiving seat removably received within said tool, said seatcomprising a seating profile for receiving a ball; wherein said seatingprofile matches a radius of said ball to nondeformably grip said ball.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a horizontal well fitted with the toolsof the present invention;

FIG. 2 is a cross sectional view of one example of the frac valve of thepresent invention in a closed position;

FIG. 3 is a cross sectional view of one example of the frac valve of thepresent invention in an opened position;

FIG. 4 is a cross sectional view of one example of the frac valve of thepresent invention in an open position with the seat drilled out;

FIG. 5 is a cross sectional view of one example of the frac valve of thepresent invention in a closed position with the seat drilled out; and

FIG. 6 is a cross sectional elevation view of a quality controlinspection fixture for use with the frac valve of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A frac valve tool is provided that improve on existing ball drop,multi-stage, horizontal fracturing tools, by providing increased safetyduring installation, reduced rig time and greater dependability infracing multiple stages in a horizontal section of the wellbore.

By combining both a slim outside diameter and short length, the presentfrac valve tool eliminates the need for handling pup joints, therebyreducing the rigidity of the liner. These features permit the moreflexible, reduced outside diameter tool string to be deployed into thewellbore with greater ease.

The present frac valve tools can be lifted by hand and hand threadedonto the liner, which is typically gripped at the rig floor, and then asection of upper liner, typically gripped in an elevator or similardevice, can lowered onto the frac valve tool and the one piece body ofthe frac valve tool allows torque to be applied from the upper linersection, through the frac valve tool and into the liner to make up theliner string.

The present frac valve tool can be deployed with associated tools alonga liner and deployed into the open hole section of the wellbore. Thepresent frac valve tools provide a means of stimulating a section of theformation to induce fracturing of the formation and flow of formationfluids. The short length of the frac valve tool 400 eliminates the needfor pup joints on either end. The small outside diameter and shortlength increases liner flexibility, further aiding deployment into thewellbore. In a preferred embodiment, the present frac valve tool 400eliminates the typical threaded connection between the top of the tooland the mandrel. Instead, a box end connection and the mandrel areintegral and an installation tool is utilized to insert the frac valvetool 400 inside the mandrel. The use of the special installation toolpermits the elimination of a threaded connection thereby shortening thefrac valve tool length.

With reference to FIG. 1, in a preferred method of deployment, thepresent frac valve tools can be deployed on a tubing string furthercomprising a float shoe or guide 50 at the toe of the liner, anactivation tool 100 at a pre-determined distance from the guide shoe 50,a first stage frac valve tool 200, and then an series comprising an openhole packer 300 alternated with the present frac valve tools 400 to afinal cased hole packer 500. It would be well understood by a person ofskill in the art that FIG. 1 merely represents one example of a tubularfracing string of tools and that additions, omissions and alterations tothe illustrated string and its components can be made without departingfrom the scope of the present invention.

The present frac valve 400 is located in the liner between two open holepackers 300 and is depicted in FIGS. 2, 3, 4, 5 and 6. The frac valve400 comprises a mandrel 420 that is preferably full bore and has aninside diameter matching the inside diameter of the liner. One or moreports 410 are formed around the circumference of the mandrel, said ports410 providing fluid communication between the inside of the liner andthe open hole wellbore. The mandrel 420 contains within it a sleeve 408connected to the mandrel by one or more shear screws 406. In a closedposition, the sleeve 408 blocks fluid passage through the one or moreports 410. Within the sleeve 408 is a seat 404 that can receive a ball402 that is deployed into the liner from the rig floor and pumped ontothe seat 404 by fluid pressure.

The present frac valve 400 is preferably pressure balanced due tosealing by o-rings that straddle the ports, such that the sleeve 408 isnot shifted to the open position until the ball 402 lands on the seat404. After the ball 402 is pumped onto the seat 404, liner pressuregenerates a force which shears shear screws 406 allowing the seat 404and sleeve 408 to shift, opening communication through the one or moreports 410.

The seat 404 of the present frac valve 400 is preferably surfacehardened to prevent erosion that can be caused by proppants pumpedthrough them. The seats 404 are manufactured from a material and in ageometry that can withstand the stress generated by the ball 402 landingand seating under high differential pressure, while providing adequatesupport for the ball 402. Suitable materials for the present seat 404may be most cast irons, including Class 40 Gray Iron or Class 50 GrayIron, although other suitable materials would be known to a person ofskill in the art and are encompassed by the scope of the presentinvention. The seats are more preferably treated with liquid nitrogen toachieve a Rockwell hardness rating of HRC 50 to 55.

The present seat preferably comprises a seating profile 416 thatreceives and in part grips the ball 402 in the seat to ensure the ball402 is not inadvertently unseated until desired. The seat radius 416 isadvantageously designed to allow gripping of the ball 402 withoutsheering the ball 402 or causing plastic deformation. The presentseating profiles requires only low pump off pressure to lift the ball402 off of the seat 404 by pressure from the formation, after fracturingis complete. This is due to the seating profile 416 being preferablymatched to a corresponding ball 402 radius to prevent the ball 402 fromdeforming and becoming wedged into the seat 404.

The relationship between the geometry of the seating profile 416 and thematching ball 402 is preferably designed to permit a variety of ball 402to seat 404 size ratios for a number of liner applications. The matchinggeometry of the seating profile 416 and the ball 402 permits a seat 404of the present design to be adapted for use with many ball and seatsizes, thereby reducing the size increments of seats 404 that need to bemanufactured. In a preferred embodiment, the size and geometry of theseating profile 416 can be adjusted relation to the size of ball 402 tobe used, this reduces potential hoop stresses that can build up in theball 402, and ensure that an optimal relationship between proper seatingand low pump off pressure.

The ball 402 used with the present invention can be any ball well knownand used in ball drop tools found in the state of the art. Morepreferably, the ball 402 is composed of a non-elastomeric material thatshows strength, corrosion resistance against stimulant fluids andwellbore fluids and a degree of flexibility. Such materials can includebut are not limited to phenolics, composites or aluminum.

The seat 404 is preferably manufactured with a minimum amount ofmaterial to allow the seat 404 to be drilled out after use, therebyminimizing drill out times. In particular, the seat material is designedto be friable and crumble upon drilling, thereby reducing the chance oflarge drilled out fragments from blocking the liner.

With reference to FIG. 4, the seat 404 of the present frac valve 400 isdrilled out after fracturing is complete. The geometry of the seat 404and the method used to fasten it to the sleeve 408 ensures the seat 404will drill up into fine particles, eliminating the possibility of largepieces of debris falling onto the next seat 404 to be drilled out. Suchdebris adds to the time required for the subsequent seat 404 to bedrilled out and tends to rotate and grind against the next seat 404.

Preferably one or more anti-rotation tabs 414 located inside the fracvalve 400 assists seat drill out by holding the seat 404 stationary.More preferably the seat 404 is threaded into the sleeve 408 in such anorientation that drilling out the seat 404 urges the threads intotightening, thereby additionally serving to hold the seat 404 in placein the sleeve 408. The threads 418 on the seat 404 and on the sleeve 408are most preferably left hand threads that tend towards tightening whenthe seat 404 is drilled. These threads 418 also allow the seats 404 ofany frac valve tool 400 to be changed as needed, for example shoulddamage be detected in a seat 404, or should on-site adjustments need tobe made for different ball and seat sizes for one or more frac valvetools 400.

In a further preferred embodiment, a quality control inspection fixture700, illustrated in FIG. 6 is used to check five dimensionalcharacteristics of each frac valve 400, to ensure correct placement ofeach valve in the liner. The quality control fixture 700 checks the borehole size through the seat 404, and the bore in which the ball 402lands. It checks the concentricity of both bores to ensure propersealing whenever the ball 402 lands on the seat 404. The quality controlinspection fixture 700 checks the geometry of the seat profile 416 andalso the distance from the seat 404 to the top of the frac valve 400, toensure proper assembly of the frac valve tool 400. The quality controlinspection fixture 700 is preferably attached to a seat installationtool (not shown) to assist in ensuring the correct seat 404 is beinginstalled into the frac valve tool 400.

In some cases, the frac valve seat 404 can be drilled out to the driftinside diameter of the liner Drift diameters are specified by theAmerican Petroleum Institute (API) for each weight of casing. An objectof a given drift diameter and given length as specified by API must fitthrough the inside diameter of the pipe.

Although it is common to run one frac valve 400 per isolated section ofthe formation, it is also possible to place multiple frac valves 400 inany given isolated section. In a preferred embodiment, the frac valve400 can be configured to have a closable feature. The closable fracvalve 400 can be closed by a number of means. One embodiment permits thefrac valve 400 to be closed before drilling out the seats, in this casea shifting tool run on tubing is used to close the frac valve 400. Asecond embodiment, illustrated in FIG. 5, allows the frac valve 400 tobe closed after the seat 404 is drilled out. Multiple frac valves 400 ora single frac valve 400 may be shifted from an open to a closed positionwith a further second style of shifting tool 412.

The total flow area through all of the fracture ports 410 of the fracvalve 400 is preferably greater than the flow area through the liner.

Sometimes a sand off occurs during the fracing operation when no moresand can be pumped into the formation and the sand remains indie theliner preventing the ability to pump the next ball down the well. Insuch cases, an opening tool (not shown) can be run through the tubingand landed on the seat 404. In such cases, applied pressure in theannular area between the inside wall of the liner and the outsidediameter of the tubing is used to pump the frac valve 400 into the openposition.

In one example of operation of the present frac valve tool 400, a linermay be assembled with a float shoe 50, an activation tool 100, a liner,a first stage frac valve tool 200, and then a series comprising a liner,an open hole packer 300, a liner and the present frac valve tools 400.Optionally, an open hole anchor may be used between the activation tool100 and the first stage frac valve tool 200 to anchor the liner to thewellbore. Alternative to an open hole anchor centralizers, stabilizersor other suitable means known in the art may also be used for thispurpose.

Preferably up to 40 frac valves 400, on a 4½″ liner for example,separated with open hole packer 300 s can be used in a string. Inoperation, the seats 404 of the frac valve tools 400 sequentiallyincrease in the size of ball 402 they can receive; with the smallestseat 404 being closest the toe end of the wellbore and the largest seat404 being at the heel end. A cased hole packer 500 is attached to theupper end of the liner. A latch seal assembly or other known means canbe used to attach the cased hole packer 500 to the work string.

The liner is run into the conditioned bore hole by a work string or on afrac string. At a predetermined depth the activation tool 100 isactivated to stop fluid flow. Pressure in the liner now increases from atriggering pressure at which both the cased hole packer 500 and the openhole packers 300 begin to set, to a final pack off pressure at which thecased hole packer 500 and open hole packers 300 are fully set. Apressure test may optionally be performed inside the casing to determineif the cased hole packer 500 has set properly. If the liner was run on awork string, the latch seal assembly or other connection means can nextbe removed from the cased hole packer 500 and the work string and latchseal assembly are removed from the well and a frac string and latch sealassembly are deployed. Otherwise, if the liner was run downhole on afrac string, no replacement has to be made.

Further pressure is applied to the fracture string. At a pre-determinedopening pressure that is higher than the pack off pressure, the firststage frac valve tool 200 shifts to the open position and stimulationfluid is pumped into the formation and causes it to fracture. Proppantis then pumped into the fracture. Next, a first ball 402 is pumped intothe liner corresponding to the seat sizes of the frac valve tool 400closest the toe of the wellbore. By this process the frac valve tool 400is activated to thereby open ports 410 to allow communication betweenthe inside of the liner and the isolated section of the formationbetween the two open hole packer 300 straddling the particular fracvalve 400. Subsequent frac valve tools 400 are similarly activated bypumping subsequent balls 402 into the liner in sequential size order.

The stimulation fluid pumped through the ports of the frac valve 400fractures the exposed formation between the open hole packers 300 usedto isolate that stage. Whenever this stage has been fractured, a nextfrac valve 400 is activated and the process is repeated. The process canbe repeated up to 40 times in total in a 4½″ liner, for example. Othersizes of liners have a different number of frac valve tools 400 and openhole packers 300. When all the desired stages have been fractured, thewell is allowed to flow and formation pressure from formation fluid flowacts to deactivate the frac valves 400 by pumping balls 402 off of theseats 404, and allows formation fluid flow into the liner. Afterwardsthe frac string and connecting means can be removed from the well.

If desired, the seats of the frac valves 400 can be drilled out at alater date.

In the foregoing specification, the invention has been described withspecific embodiments thereof; however, it will be evident that variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the invention.

1. A frac valve tool, said tool comprising: a. one or more ports; b. asleeve movable between a closed position in which the sleeve preventsfluid flow through said one or more ports and an open position in whichthe sleeve allows fluid flow through said one or more ports; and c. aball receiving seat removably connected to the sleeve; wherein receiptof a ball on the ball receiving seat moves said seat and said sleevefrom closed to open positions.
 2. A frac valve tool, said toolcomprising a ball receiving seat removably received within said tool,said seat comprising a seating profile for receiving a ball; whereinsaid seating profile matches a radius of said ball to nondeformably gripsaid ball.
 3. The frac valve tool of claim 1, wherein the seat furthercomprises a seating profile to receive and grip the ball.
 4. The fracvalve tool of claim 3, wherein the seating profile has a geometry thatnon-deformably grips the ball.
 5. The frac valve tool of claim 4;wherein the removable seat is changeable to accommodate more than onesize of seat and more than one size of ball in the tool.
 6. The fracvalve of claim 1, further comprising one or more shear screws affixingthe sleeve to the tool, said shear screws being shearable at apredetermined liner pressure accumulated in the tool when the ball landson the seat, wherein shearing of said one or more shear screws allowsthe seat and sleeve to shift to the open position.
 7. The frac valvetool of claim 6, further comprising a mandrel within which the sleeve ismovably affixed via the shear screws and through the circumference ofwhich the one or more ports are formed.
 8. The frac valve tool of claim1, wherein the total flow area through all of the one or more ports isgreater than the flow area through the liner.
 9. The frac valve tool ofclaim 1, wherein the seat is a drillable seat.
 10. The frac valve toolof claim 9, wherein the drillable seat is made of a friable materialthat crumbles upon drilling.
 11. The frac valve tool of claim 10,wherein then seat is composed of a cast iron.
 12. The frac valve tool ofclaim 11, the seat is surface hardened
 13. The frac valve tool of claim12, wherein the seat has a Rockwell hardness rating of HRC 50 to HRC 55.14. The frac valve tool of claim 1, further comprising a closablefeature.
 15. The frac valve tool of claim 14, wherein the frac valvetool is closable before the seat is drilled out.
 16. The frac valve toolof claim 14, wherein the frac valve tool is closable after the seat isdrilled out.
 17. The frac valve tool of claim 1, further comprising oneor more anti-rotation tabs inside the frac valve tool to stabilize theseat against rotation during drill out.
 18. The frac valve tool of claim17, wherein the seat is threadably affixed into the sleeve in adirection that serves to tighten against rotation during drill out. 19.The frac valve tool of claim 18, wherein the seat is left hand threadedinto the sleeve and tend towards tightening when the seat is drilled.20. The frac valve tool of claim 1, further comprising a quality controlinspection fixture to inspect dimensional one or more characteristics ofthe frac valve tool.
 21. The frac valve tool of claim 20, wherein thequality control inspection fixture inspects bore hole size through theseat, the bore hole of seating profile, concentricity of both bore holethrough seat with bore hole through seating profile, geometry of theseat profile and distance from the seat to a top surface of the fracvalve tool.
 22. The frac valve tool of claim 21, wherein the qualitycontrol inspection fixture is attached to a seat installation tool toinstall a predetermined seat into the frac valve tool.